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Proceedings of the American Mathematical Society
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A short proof of a conjecture on the connectivity of graph coloring complexes

Author(s): Alexander Engström
Journal: Proc. Amer. Math. Soc. 134 (2006), 3703-3705.
MSC (2000): Primary 57M15, 05C15
Posted: June 12, 2006
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Abstract: The $ {\tt Hom}$-complexes were introduced by Lovász to study topological obstructions to graph colorings. It was conjectured by Babson and Kozlov, and proved by Cukic and Kozlov, that $ {\tt Hom}(G,K_n)$ is $ (n-d-2)$-connected, where $ d$ is the maximal degree of a vertex of $ G$, and $ n$ the number of colors. We give a short proof of the conjecture.


References:

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E. Babson, D.N. Kozlov, Complexes of graph homomorphisms. Israel J. Math. 152 (2006), 285-312.

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A. Björner, Topological Methods, in: ``Handbook of Combinatorics'' (eds. R. Graham, M. Grötschel, and L. Lovász), North-Holland, 1995, 1819-1872. MR 1373690 (96m:52012)

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S. Lj. Cukic, D.N. Kozlov, Higher connectivity of graph coloring complexes, Int. Math. Res. Notices. 2005:25 (2005), 1543-1562.MR 2152894

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R. Forman, Morse theory for cell complexes, Adv. Math. 134, no. 1, (1998), 90-145.MR 1612391 (99b:57050)

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D.N. Kozlov, Chromatic numbers, morphism complexes, and Stiefel-Whitney characteristic classes, 67 pages, to appear in Geometric Combinatorics, IAS/Park City Mathematics Series 14, American Mathematical Society, Providence, RI; Institute for Advanced Study (IAS), Princeton, NJ.


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Additional Information:

Alexander Engström
Affiliation: Department of Computer Science, Eidgenössische Technische Hochschule, Zürich, Switzerland
Email: engstroa@inf.ethz.ch

DOI: 10.1090/S0002-9939-06-08417-6
PII: S 0002-9939(06)08417-6
Keywords: Graph homomorphisms, $k$-connectivity, {\tt Hom}-complexes, graph coloring complexes
Received by editor(s): May 31, 2005
Received by editor(s) in revised form: July 6, 2005
Posted: June 12, 2006
Additional Notes: This research was supported by ETH and Swiss National Science Foundation Grant PP002-102738/1
Communicated by: Paul Goerss
Copyright of article: Copyright 2006, American Mathematical Society
The copyright for this article reverts to public domain after 28 years from publication.


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